A security monitoring system is a field that has been researched for a long period of time. Recently, an intelligent security system technology has been actively researched. As the related art, there are a security camera type, an infrared (IR) type, an ultrasonic type, an acoustic measurement type, or the like.
The first related art, U.S. Pat. No. 7,535,351 (Acoustic intrusion detection system) discloses a technology of detecting whether the trespassers are intruded by comparing and sensing the difference between a magnitude and a phase of a sound wave generated from the trespassers and a magnitude and a phase of a sound wave before the intrusion of the trespassers by generating acoustic in an audible frequency domain from a bipolar emitter and disposing a pair of detectors in an acoustic offset null of the bipolar. The related art is restrictively used in a specific security zone to detect only whether the trespassers are intruded but it cannot monitor positions or movements of the trespassers.
The second related art, Korean Patent Application Laid-Open No. 2008-0055340 (System and method for intrusion sensing and alarm using ultrasonic wave for vehicle) discloses a technology of detecting an intrusion of a vehicle by using an ultrasonic wave. The related art is a technology relating to a system and a method for intrusion sensing and alarm using ultrasonic wave for vehicle that digitally modulates an ultrasonic wave and reduces erroneous detection due to echo or noise from the outside to improve detection precision, which may solve malfunction due to an ultrasonic wave from other vehicles. However, the related art may degrade power efficiency according to the use of an ultrasonic wave and may lead to errors such as generating intrusion signals regardless of whether the trespassers are intruded when an ultrasonic waveform is distorted due to objects or conditions in any space.
The third related art, Korean Patent Application Laid-Open No. 2004-0025148 (Apparatus and method for security using an environmental sound) discloses a technology of monitoring whether abnormality occurs in places to be monitored by using environmental sound generated according to environment of predetermined places to be monitored. The related art discloses a method of disposing a detector in the predetermined places to be monitored to allow a feature extractor to extract predetermined characteristics from an acoustic signal, allowing an abnormality occurrence determination unit to compare the extracted features with an environmental acoustic reference model stored in a memory to determine whether abnormality occurs in the predetermined places, and if so, allowing an alarm output unit to generate an alarm signal so as to issue an alarm to a supervisor. The related art may not operate the monitoring device at the time of the intrusion of trespassers since the environmental sound is not changed when trespassers or intrusion objects are calmly intruded.